The sequel was announced in May 2012, after the successful release of The Avengers. Whedon, the director of the first film, was brought back on board in August 2012 and a release date was set. By April 2013, Whedon had completed a draft of the script. Casting began in June 2013 with the re-signing of Robert Downey, Jr. The film is scheduled to begin principal photography in early 2014 at Shepperton Studios in Surrey, England. Additional footage is also scheduled to be filmed in the United States, Italy and South Africa.
Avengers: Age of Ultron is scheduled for release on May 1, 2015.
An artificial intelligence overwhelmed with a god complex and a rage toward his creators, who longs to take over the Earth with his own spawn. Joss Whedon stated that Spader was his "first and only choice" for the role, because of his "hypnotic voice that can be eerily calm and compelling" while also being very human and humorous. Producer Kevin Feige clarified, "We'll be capturing his face and his body to create a whole performance... We did not hire James Spader to do a robot voice." About the character Whedon said, "He’s always trying to destroy the Avengers, goddamn it, he’s got a bee in his bonnet. He’s not a happy guy, which means he’s an interesting guy. He’s got pain. And the way that manifests is not going to be standard robot stuff." Whedon also indicated that some of Ultron's abilities from the comics would be stripped.
The twin sister of Quicksilver, who has telekinetic abilities and can weave spells. Olsen described the character as a "nexus", elaborating, "She's crazy. She has more things wrong with her than any character I've ever played. She can tell you where an object has been, she can tell you what your future is, she can connect with the dead and people from the past, the future, other universes, and she's the only person in this universe who's capable of doing that. She's unbelieveable."
The twin brother of the Scarlet Witch, who can move at superhuman speed. About the character Taylor-Johnson said, "Him and his sister [Scarlet Witch] have been abandoned by their parents and their father, and they grew up in Eastern Europe defending and looking out for themselves and each other... His sister really is his guidance - emotionally she's the one who looks after him, and vice versa. He's very overprotective physically - he doesn't want anyone touching her." Taylor-Johnson also said that Quicksilver has "real anger frustration" and is easily bored due to a short attention span.
In October 2011, Feige said during the New York Comic Con, "Iron Man 3 will be the first of what we sort of refer to as phase two of this saga that will culminate, God willing, in Avengers 2". In March 2012, Joss Whedon, director of the first film, stated that he would want a sequel to be "smaller. More personal. More painful. By being the next thing that should happen to these characters, and not just a rehash of what seemed to work the first time. By having a theme that is completely fresh and organic to itself." At the premiere of The Avengers, Feige said the studio had an option for Whedon to return as director. In May 2012, after the successful release of the first film, Disney CEO Bob Iger announced a sequel was in development. Most of the film's cast members were under contract to potentially appear in the sequel; however, Robert Downey, Jr. was not, as his four picture deal with Marvel would expire after Iron Man 3.
At the 2012 San Diego Comic-Con International, Joss Whedon said he was undecided about directing, stating, "I have not come to a decision on directing Avengers 2. I am having too much fun with this [Firefly reunion] now." However in August 2012, Iger announced that Whedon would return to write and direct the sequel and develop the Marvel television series, Agents of S.H.I.E.L.D., for ABC. Later in the month, Disney set a May 1, 2015 release date. Asked about his decision to return, Whedon said "Avengers 2, it wasn’t a tough decision. For a long time I thought, 'Well, it’s just not going to happen.' Then when I actually started to consider it, it became so clear that I desperately wanted to say more about these characters, it wouldn’t’ve been an easy no and it was a spectacularly easy yes. There was no wrestling." Whedon said that they intended for the film's production to not be as rushed as the first one. In a December 2012 interview with Entertainment Weekly, Whedon stated that he had completed an outline for the film.
In April 2013, it was reported that filming was scheduled to begin in early 2014 at Shepperton Studios in England. At the Hollywood premiere of Iron Man 3, Whedon said that he completed a draft of the script, and had started the storyboard process and to meet with actors. Whedon also mentioned that he wrote with Downey in mind and included a "brother/sister act" from the comic books.Entertainment Weekly reported that Whedon was referring to Quicksilver and the Scarlet Witch, which Whedon confirmed. During an appearance on Late Night with Jimmy Fallon, Whedon explained his rationale for including the characters in the film: "Besides the fact that I grew up reading them, their powers are very visually interesting," said Whedon. "One of the problems I had on the first one was everybody basically had punchy powers... [Quicksilver]’s got super speed. [Scarlet Witch] can weave spells and a little telekinesis, get inside your head. There’s good stuff that they can do that will help sort of keep it fresh."
In May 2013, The Hollywood Reporter reported that Downey was in negotiations to extend his contract with Marvel Studios and reprise his role as Iron Man in the film, as well as a third Avengers film. Also in May, the chairman of Cape Town Film Studios said that Marvel Studios was interested in shooting the film in Cape Town, South Africa. In June 2013, Variety reported that Aaron Taylor-Johnson had entered talks to play Quicksilver, which Taylor-Johnson confirmed in a July 2013 Collider interview. Later in June, Downey signed on to return as Iron Man for the film and a third Avengers film. Marvel also announced that filming was expected to begin in March 2014.
At the 2013 San Diego Comic-Con International, Whedon announced the film would be subtitled Age of Ultron. Despite the subtitle, the film is not based on the 2013 comic book miniseries Age of Ultron. Feige explained, "We came up with a few titles, but every month a new comic book appeared, and that's a great title. Age Of Ultron is a great title. We had a few other 'Of Ultrons', but that was the best one. So we're borrowing that title, but taking storylines from decades of Avengers storylines." Whedon added, "We're doing our own version of the origin story of Ultron....We were crafting our own version of it where [Ultron's] own origin comes more directly from the Avengers we already know about. The other thing is in the origin story there was Hank Pym, so a lot of people assumed he was going to be in the mix, but he's not. We're basically taking the things from the comics for the movies that we need and can use. A lot of stuff has to fall by the wayside." Whedon also said the film would have a darker tone due to Ultron's involvement, and confirmed that Hawkeye and Black Widow would return. The title of the film came as a surprise to many fans who were expecting Thanos, the mastermind behind the events of the first film, to be the main villain in the sequel. When asked about Thanos' involvement, Whedon responded, "We have to stay grounded. It's part of what makes the Marvel universe click - their relationship to the real world. It's science fiction, and Thanos is not out of the mix, but Thanos was never meant to be the next villain. He's always been the overlord of villainy and darkness."
In September 2013, Chris Hemsworth and Scarlett Johansson confirmed they would be returning as Thor and Black Widow respectively, with Johansson mentioning that filming would begin in January. Also in September, extensive scans were taken of Spader's head and body in preparation for the role. In October 2013, Samuel L. Jackson confirmed that Elizabeth Olsen had been cast as the Scarlet Witch, while The Wrap reported that Taylor-Johnson closed the deal to play Quicksilver after working out scheduling conflicts in promoting his appearance in the 2014 Godzilla reboot. Marvel later officially confirmed Olsen and Taylor-Johnson in November 2013.
In November 2013, Cobie Smulders confirmed in an interview that she is reprising her role as Maria Hill. Also in November, Feige commented on finding the right balance between technology and fantasy based heroes in Avengers: Age of Ultron saying, "Iron Man is a very technological hero his movies are always technologically based. The first Thor was all about introducing Asgard and Thor in that more fantastical realm into the more reality-based MCU, and explain that obviously it might look like magic, but it's another form of science and technology. As we go into Ultron clearly he does come out of technology, but we're using all of our tools at our disposal that we've established so far as part of the MCU to build the storyline of Age of Ultron. At the end of the month, Screen Rant reported that portions of the film would also be shot in the United States. In December 2013, USA Today reported that Don Cheadle will have a part in the film.
In January 2014, Thomas Kretschmann was cast as Baron Wolfgang von Strucker. On January 24, 2014, while promoting the French release of Much Ado About Nothing, Whedon spoke about the continuity of the film saying, "I have to make my movie assuming that people will only have seen the first one, or possibly not even seen the first one. I can't assume that everybody went to see Thor [The Dark World], Captain America [The Winter Soldier], and Iron Man  in-between. I have to go from one movie to the next and be true to what's happened, but not be slavish to it... The model I'm always trying to build from, my guiding star, is The Godfather: Part II where a ton has happened in-between and it's a very different movie [from Part I], but you don't need any information: it's there in the film." On the same day, the Forte di Bard Association announced that filming would take place at Fort Bard in the Aosta Valley region of Italy in March 2014, as well as other locations throughout Aosta, Donnas, Bard, Pont-Saint-Martin and Verrès. In February 2014, the Gauteng Film Commission announced that action sequences would be filmed in Johannesburg, South Africa and other locations in Gauteng, beginning in mid-February.
Footage of the 2013 Comic-Con teaser, as well as a brief interview with Joss Whedon, was made available as part of Iron Man 3's second screen companion app for its Blu-ray release on September 24, 2013.